Concrete is a blend of cement material, aggregate, and water. Aggregate known as inert filler comprising 60 to 80 percent of the volume and 70 to 85 percent of concrete’s weight. In Better concrete mix, aggregates must be clean, hard, free from chemicals and coating of other materials like clay and other which can cause weakening of concrete. Aggregates strongly influence concrete’s freshly mixed and hardened properties, mixture proportions, and economy.
It is having diameter lesser than 4.75 mm. Fine aggregate described as:
Natural Sand–Resulting from the natural breakdown of rock
Crushed Stone Sand– It is produced by crushing hard stone.
Crushed Gravel Sand– It is produced by crushing natural gravel.
It is greater than 4.75 mm. Coarse aggregate described as:
Uncrushed Gravel or Stone– It produced from natural disintegration of rock
Crushed Gravel or Stone– It produced from crushing of gravel or hard stone.
Sand is molded by the weathering of rocks. The classification of sand based on the origination category: –
PIT SAND: – This sand is obtained by founding pits in soils. It is quarried from a depth of about 1-2 m from the ground level. This sand is found as credits in soil and it consists of sharp angular grains, which are free from salts. It is used as an excellent material for mortar or concrete work. Pit sand must be made free from clay and other organic materials before it can be used in mortar
RIVER SAND: – It is found on the beds of rivers and it consists of fine rounded grains. The presence of fine rounded grains is due to mutual attrition under the act of water current.
SEA SAND: – It is found on the sea shores. It is brownish and fine rounded grain. As it is obtained from sea it contains salt, which is used in attracting moisture from atmosphere. Such absorption causes dampness and disintegration of work. It is generally not used for engineering purpose due to its retards setting action of cement. It is normally used for non-structural purposes.
Crushed Stone Sand / Artificial Sand :-It is used as the substitute for River Sand, fine aggregates which manufactured by crushing either granite or basalt rock.
Types of Gravels
|Bank gravel||natural gravel mixed with sand or clay found near by rivers and streams.|
|Crushed stone||rocks are crushed and they are then graded by screens and then it is mixed to a blend of stones and fines. It is widely used as a surfacing for roads and driveways.|
|Fine gravel||gravel consisting of particles having 2 to 4 mm diameter|
|Pea gravel||gravel that consists of small, rounded stones used in concrete surfaces. Also used for walkways, driveways and as a substrate in home aquariums|
|Lag gravel||It is produced by the removal of finer particles.|
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